Gelatin filaments and preparation thereof



April l945- H. HIGHBERGER 'ETAL 2,374,201

GELATIN FILAMENTS AND PREPARATION THEREOF Filed Sept. 15, 1941 1N VENT OR.

ATTO R N EYS.

Patented Apr. 24,1945

. GELATIN FILAMENTS AND PREPARATION THEREOF John H. Highberger and Harold J. Kersten, Cincinnati, Ohio, assignors to Foundation of The Research Laboratory of The Tanners Council of the UnitedStates of America at the University of Cincinnati, Inc., Cincinnati, Ohio, a corporation of Delaware Application September 15, 1941, Serial No. 410,852

11 Claims.

This application is a continuation in part of our copending application, Serial No. 357,664, filed September 20, 1940, and entitled Gelatin filaments and preparation thereof.

Our invention relates to the preparation of filaments of collagen or gelatin, the essential feature of which is the coagulation of the gelatin in filament form from jets of a solution thereof in such a way as to recreate the fibrous nature thereof in an orientation generally lengthwise of the filaments, thus closely simulating the orientation existing in nature in the original tissue.

Various suggestions have been made in the past whereby gelatin could be formed into filaments and by a tanning action rendered insoluble to the desired degree. In our practice we follow the filament formation with tanning action, but due to the fibre orientation we obtain a strength which so far as we are advised, is not obtainable by prior practice.

The objects of our invention, as set forth above, or as will be pointed out hereinafter, we accomplish by that certain procedure and in that product of which we shall describe exemplary embodiments. Reference is made to the drawing wherein Figure 1 illustrates diagrammatically an apparatus which we may use.

Figure 2 is an X-ray diffraction pattern.

To describe our preferred practice, we find it most desirable to prepare our gelatin from fresh hides rather than to use scraps of hides which have been limed. Commercial gelatin which is made from such hides as a by-product of the leather industry gives good results according to our practice, but not as good as where we derive the gelatin from fresh or unlimed hides.

Where hides are limed the gelatin resulting from extraction has an iso-electric point of less than 5. However when the gelatin is not produced by liming, such as by extraction in plain water or in acidulated water, the iso-electric point runs to a point between 6 and 8. The gelatin which we employ and as described consisting of gelatin from unlimed hides has the iso-electric point between 6 and 8.

We first clean the hide and using the inner layer, derive the gelatin by removal of extraneous material by the usual mechanical technique. The collagen is then converted to gelatin by the use of water with or without alkali or acid, the alkali not being employed in such quantity as to produce a limed type extraction.

Concentration of gelatin in the gel should be above five per cent. We get our most favorable results with concentration of ten to eighteen parts by weight of gelatin to ninety to eightytwo parts of water by weight.

Having formed the gel we render the same liquid by application of heat or the heat may be applied as a part of tire first stage, and then in one procedure force the liquid in jets of desired fineness into a coagulating bath. This bath may be in general a water solution of any agent which has the property of coagulating a protein although high boiling point water miscible coagulating agents give the best results. Ethyl alcohol and acetone are not very satisfactory. We have found excellent results to follow from the use of a saturated solution of sodium citrate. A saturated solution of ethylene glycol mono ethyl ether, not hitherto employed as a coagulant as far as we are advised, is excellent in its action in our process. We have used with good results diacetone alcohol and acetonyl acetones.

The jets of liquid are reacted upon to assume fibrous form very rapidly, thirty seconds in the bath being satisfactory. Thus by controlling the velocity of the jets and the length of the travel in the bath, it will be simple to control the speed of production. The coagulated filaments are drawn from the bath by driven rollers, and these rollers are operated at a speed which puts a stretch in the filaments. This stretching during the coagulation is of primary importance for producing the parallelism of orientation of the micelles of fibres during the coagulation reaction.

Fig. 1 shows in diagram an apparatus which will be satisfactory for following out our process although many forms of apparatus could be used. In this diagram I illustrates a nozzle for extruding filaments .of gelatin. The bath of coagulant is contained in the vessel 2. Within this vessel are drums, in this instance drums 3, 4, and 6, the drum 5 being above the vessel. The drums are of different size, growin'g progressively of greater diameter and they are rotated the same number of revolutions per minute, whereb each has a faster surface speed than the other. The filaments indicated at l, are passed around each drum. The resulting stretched threads are accumulated in any suitable manner. The diametc! of the final filament depends upon its original extruded thickness.

Fig. 2 is a diagram showing the X-ray difiraction patterns of a native collagen fibre. In this diagram, the thickening at two opposed areas of the second ring 8, and the presence of the sharply defined ring lines 9, 9, in the third ring,

on an axis normal to the axis of the thickened areas of the second ring, are noteworthy. The fibres produced by our practice as herein described will show the typical X-ray diffraction pattern illustrated.

We find that we can treat the filaments as they come from the coagulating bath so as to render them physically comparable to filaments of cat gut," made from sheep intestines. In the stretched coagulated form the fibrous structure is decidedly of parallel orientation in the fibres thereof, as shown by the X-ray diffraction pattern produced, which is very similar to that produced from native collagen fibre.

From the coagulating bath the filaments are passed through a tanning bath. The technique of tanning the filaments is not different from that of tanning leather. We find it desirable, however, to use in the tanning bath sufficient of the coagulant to prevent swelling of the fibres. As an illustration, we have used in obtaining a fibre highly resistant to water, five percent formaldehyde in a saturated solution of sodium citrate or of ethylene glycol mono ethyl ether, at room temperature. The filaments so treated will wet with boiling water, but will not hydrate and will return to their former condition after drying.

We can control the tanning period to give different degrees of water resistance, using known technique, for example we can parallel the condition of cat gut as used in surgical sutures, the outstanding difference in our product being that it is of unlimited length of the intestines from which they are made. We have used alcoholic solutions of tannic acid and vegetable tannins with good results.

Mechanical polishing can be imparted to the fibre by practice similar to rayon technique; and the thickness of the fibre can be controlled within limits of coagulating and tanning time. Ordinarlly it has been planned to make the finer filaments and spin them to derive the desired thickness.

We have been able with a longer time of treatment to combine the coagulating and tanning step, using the second bath (above described, as an example), as the only treatment bath. This takes more time and would probably complicate the mechanical apparatus for continuous production rather than simplify it. The stretching of the filaments as they coagulateis practiced here as before. Other ways are practical for obtaining the fibre orientation of natural cat gut, and hence its strength and durability. Thus, permitting the filaments as extruded to coagulate in the air will be practical and sufficient if they are stretched before solidification has taken place. As a means of stretching the filaments whether as they pass through the air or through a coagulating bath, we employ satisfactorily a drum around which the filaments are'given one or more wraps. From this drum the filaments are passed around another drum which is rotating at a higher speed. It is necessary to use, in this case, a more concentrated gelatin solution than in the preceding. In general this should not be below 25% by weight, and depending on the gelatin in use, and other factors, we find it works best at concentrations between 25 and 50%, that is, 25 to 50 parts of dry gelatin to 75 to 50 parts of water. Glycerine in small amounts may or may not be added.

If the filaments are stretched less than three times their original length (or not reduced to at least A of their original diameter), the fibre orientation will be of undesirable strength. Furthermore, this stretching must take place during the setting or coagulation of the extruded filaments. The upper limit of stretch is that which will not break the filaments. we have used stretches up to five times the original length.

The small diameter threads produced by our practice can be promptly spun into threads of any desired diameter. They differ from natural cat gut in that their length is not restricted, as is the case with a natural gut whose length is determined by the animal intestine from which they are cut. The air coagulated threads can be tanned as desired just as those which are chemically coagulated.

The fibre X-ray diagram of our product will be similar to that of natural cat gut and the fineness thereof is not limited by the difficulties attendant upon cutting of natural gut, any more than is the length thereof.

By our discussion of the desirable purity of our gelatin, we do not wish to be construed as limiting our invention thereto.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. A filament of unlimited length derived from gelatin having a fibre orientation typical of that produced by stretching a jetted filament of gelatin solution of greater than around ten percent concentration of gelatin in water by weight, to more than four times its length as Jetted while the micellae thereof are free to change orientation.

2. A tanned filament of unlimited length derived from gelatin having a fibre orientation typical of that produced by stretching a jetted filament of gelatin solution of greater than around ten percent concentration of gelatin in water by weight, to more than four times its length as jetted while the micellae thereof are free to change orientation.

3. A filament of unlimited length derived from gelatin having a fibre orientation typical of that produced by stretching a jetted filament of gelatin solution of greater than around ten percent concentration of gelatin in water by weight, to more than four times its length as jetted while the micellae thereof are free to change orientation, the said gelatin being derived from hides which have not been previously limed.

4. The process of forming filaments which consists in forming a liquefied gel of gelatin, jetting the liquid, causing the jetted filaments to coagulate, and while the jets are coagulating stretching the filaments fonned by letting to a diameter at most four-sevenths of the jetted diameter.

5. The process of forming filaments which consists in forming a liquefied gel of gelatin by heat, jetting the liquid into a coagulating bath, the said gel containing more than five percent by weight of gelatin and continuously subjecting the filament to tension sufilcient to increase its length more than three times, while the micellae are free to change orientation, and the filament also being treated with a tanning solution in the presence of coagulant.

6. The process of forming filaments which consists in removing the gelatin from fresh hides, forming a water solution thereof of greater than around five percent by weight of gelatin, and while hot and hence liquid jetting the solution to form filaments, coagulating the filaments and continuously stretching the filament resulting from coagulation of said liquid let during the coagulation step to more than four times its original length, and the filament also being treated with a tanning solution.

7. The process of forming filaments of controlled water sensitivity which comprises forming a liquid water solution of gelatin under heat of a concentration of at least 5% gelatin by weight, and jetting the solution into a bath containing a coagulant for the gelatin, the coagulant being ethylene glycol mono ethyl ether.

8. The process of claim 7 wherein the coagulant bath also contains a tanning agent for controlling th ultimate solubility of the resulting filament.

9. A filament of unlimited length derived from gelatin having a fibre orientation typical of that produced by stretching a jetted filamcntoizelatin solution of greater than around ten percent concentration of gelatin in water by weight, to more than four times its length as jetted while the micellae thereof are free to change orientation, the X-ray diffraction pattern of the filament being substantially that of native cat gut made from sheep intestines.

10. A tanned filament of unlimited length derived from gelatin having a fibre orientation typical of that produced by stretching a jetted filament of gelatin solution of greater than around ten percent concentration of gelatin in water by weight, to more than four times its length as jetted while the micellae thereof are free to change orientation, the X-ray difi'raction pattern of the filament being substantially that of native cat gut made from sheep intestines.

11. A filament of unlimited length derived from gelatin having a fibre orientation typical of that produced by stretching a jetted filament of gelatin solution of greater than around ten percent concentration of gelatin in water by weight, to more than four times its length as jetted while the micellae thereof are free to change orientation, the said gelatin being derived from hides which have not been previously limed, the X-ray diffraction pattern of the filament being substantially that of native cat gut made from sheep intestines.

JOHN H. HIGHBERGER. HAROLD J. KERSTEN. 

